I discuss the prospects of gravitational wave astronomy around 0.1-10
Hz. This frequency regime is just between the two bands probed by
ground-based detectors (LIGO, Virgo, KAGRA,..) and the proposed space
detectors (LISA, TianQin, Taiji). I briefly introduce the Japanese
plan DECIGO targeting this band and then discuss its main science
targets, including primordial stochastic background and compact
binaries.
